Process for forming hard oxide pellets and product thereof



Jan. 7, 1969 v, ME ET AL PROCESS FOR FORMING HARD OXIDE PELLET S ANDPRODUCT THEREOF Sheet Filed Sept. 2, 1966 Pelletizer lNVENTORS ValentineMekler Morgan C. Sze

Ward J. Bloomer William V. Bauer BY 773mm, 2W

Fig. l.

ATTORNEYS Jan. 7, 1969 PROCESS FOR FORMING HARD OXIDE PELLETS ANDPRODUCT THEREOF Filed Sept. 2, 1966 Sheet 3 of 3 9 re 8 7 ea c e 400 Heater m Pelletizer 400 Pellet 750 Heater Ggs sml Muffle 5 Gasolme J CokerI000 Distillate A J Muffle 6 o a clnar Calciner I600 A Coker Gas 7 rHeavy Oil |soo J Reducer i 2ooo L 2 2z ,J Air 7 Water Steam Flue Gas2000 Boiler ||5 Air Heater INVENTORS Valentine lgekler Morgan 0. ze Flg.4. War d .1. Bloomer Wilham V. Bauer BY 77Za/z/n &

ATTORNEYS United States Patent 3,420,656 PROCESS FOR FORMING HARD OXIDEPELLETS AND PRODUCT THEREOF Valentine Mekler, New York, and Morgan C.Sze, Garden City, N.Y., Ward J. Bloomer, Westfield, N.J., and William V.Bauer, New York, N.Y., assignors to The Lummus Company, New York, N.Y.,a corporation of Delaware Filed Sept. 2, 1966, Ser. No. 577,055 .U-S.Cl. 75.5

Int. Cl. C21b 1/10 20 Claims ABSTRACT OF THE DISCLOSURE This inventionrelates generally to a process for agglomerating, hardening andpartially reducing an oxide ore prior to its introduction into ametallurgical furnace. More specifically, the invention relates to thetreatment of iron oxide ores, such as taconite fines, by agglomerationat 400500 F. using a heavy oil residue as binder, coking at 700l000 F.,and hardening and reducing at 1500-2200 F., preferably below about 2100F. The invention also relates to the pellets themselves, which arereduced about 1540%, with some metallic iron and with little or no freecarbon. Partial reduction per se is not the main objective of theinvention, but it does provide the crushing strength necessary for blastfurnace usage, and of course the reduction raises blast furnaceefliciency. I

As is well known in the art, pig iron is produced from iron ore, cokeand limestone introduced into a blast furnace. At the point of entry ofthe air into the blast furnace, high temperatures are attained as aresult of the exothermic heat of combustion of coke with air. The carbonmonoxide formed by the incomplete combustion of coke and unburned cokereduce the iron oxide to iron. Impurities present in the ore and cokeform a slag with the limestone. Molten pig iron and slag areperiodically removed from the hearth of the blast furnace.

Since the blast furnace is a shaft furnace, it is necessary that theore, coke and limestone be aggregates of fairly large particle size. Theamount of fines in the charge materials should be minimized since finescan be blown out of the furnace as dust and can also plug up the shaft,thereby resulting in a high pressure drop. A number of factors are ofimportance in regard to the materials charged to the furnace. Forexample, since metallurgical coke is relatively expensive, it is obviousthat the amount required per ton of product should be minimized.Furthermore, lower coke requirements reduce the amount of ash necessaryto be slagged out, andthereby reduce the amount of limestone required to.be introduced into the blast furnace, consequently resulting in higherfurnace capacity and lower production cost per ton of product.

Recently, taconite ore-a low-grade iron oxide ore has been increasinglymined as a result of decreasing supply of high grade ores. Beneficationof taconite usually involves grinding the ore to form very small iceparticles of fines, followed by magnetic separation of iron values (Fe OThe fines are agglomerated into pellets prior to charging the ore into ablast furnace. Agglomeration of the ore generally consists ofpelletizing or briquetting the fines with the assistance of a bindingagent, and then heating the resulting material to a high sinteringtemperature in the order of 2200 2400 F., to increase the strength ofthe pellets. In commercial pelletizing plants, bentonite clay and somesolid carbonaceous fuel are added to the concentrate. The mixture isthen passed through a balling drum (where the wet bentonite-concentratemixture is made into balls of, for example, A to size); a vibratingfeeder and a sintering machine wherein, at a temperature ofapproximately 2350 F., hardened pellets are produced. The pellets arethereafter cooled, screened and stored for shipment.

Briquetting differs from pelletizing only in that the binder-ore mixtureis formed into shape by pressing rather than by balling, as for examplein briquetting rolls, or by extrusion.

Several disadvantages characterize the present practice of pelletizing.High sintering temperatures are required to provide hardness and highstrength to the pellets consequently using substantial quantities offuel. Such pellets are not large aggregates and therefore high blastrates in the furnace cannot be used. This is especially so, since thesize of the pellets is much smaller than the size of the coke andlimestone used. The optimum size range of the pellets should be near thesize range of the limestone and coke. Additionally, the use of anash-containing carbonaceous fuel to supply the heat for agglomerationincreases the amount of slag which has to be produced. Since thefinished pellets are not reduced at all, they cannot effect any savingin metallurgical coke requirements. Highly reduced pellets are producedby various processes, all of which use solid carbonaceous fuels forreduction and for heat. The pellets have varying amounts of residualcarbon. The ash content is inversely related to the qualityand costofthe solid fuel.

Numerous procedures have been proposed to overcome disadvantages of thecharacter indicated above. For example, it has been proposed to use atar oil or a petroleum oil with an iron oxide concentrate, rather than asolid carbonaceous fuel, but strong, reduced pellets were not produced.It has also been proposed to use an asphalt with an oxide ore; however,even when temperatures of the order of 1500-l600 F. are used in forminga carbon-impregnated oxide ore aggregate, little physical strength isdeveloped. A further proposal of prior workers was to initially mix theore with tar at the mine site to render it non-dusting. At the steelmill, it Was mixed with powdered coal and this mixture was briquettedand carbonized. Of course the coal addition brings back the ash problemnoted above. Accordingly, while a number of such proposals have beenmade, there has been little or no success in providing oxide ore pelletshaving sufi'icient hardness to withstand the rigor of mechanicalhandling and thermal shock before and after being introduced to anagglomerating furnace. Nor has there been success in reducing the fuelrequirements in preparing such agglomerates, or the ash content of thepellets.

It is an object of the present invention, therefor, to provide a processfor forming oxide ore in pellet form of desired strength and hardness,of suitable size for efiicient use in a metallurgical furnace, and oflow ash content.

It is another object of the invention to form such pellets at relativelylow temperatures and at an economical level of fuel consumption.

A further object is to provide partially reduced iron oxide ore inpellet form of said desired characteristics, whereby blast furnace cokerequirements are reduced.

Another object of the invention is to provide iron oxide ore in pelletform containing low residual free carbon.

Still another object of the invention is to provide a process forforming oxide ore pellets utilizing inexpensive carbonaceous materials.

Yet another object of the invention is to provide a hard, partiallyreduced iron oxide pellet having the abovenoted characteristics.

Various other objects and advantages of the invention will become clearfrom the following description of several embodiments thereof, and thenovel features will be particularly pointed out in connection with theappended claims. The description will refer to the accompanyingdrawings, which are illustrative only and should not be interpreted in alimiting sense, and in which:

FIGURE 1 is a greatly simplified, pictorial flow sheet depicting theessential elements of the process as carried out in illustrativeapparatus;

FIGURE 2 is a greatly simplified, schematic flow sheet depicting thesolids flow in a second embodiment of the invention;

FIGURE 3 is a great-1y simplified, schematic flow sheet depicting thesolids flow and liquid recovery in an embodiment of the inventiondesigned to product 3000 t.p.d. of product pellets; and

FIGURE 4 is a simplified, schematic flow sheet depicting gas and liquidflows for the embodiment illustrated in FIGURE 3.

While the description made herein of the invention is primarily directedto the treatment of iron oxide ores, it is to be understood that otheroxides ores can be treated.

The foregoing objects are realized by a process comprising the followingsteps:

(a) Mixing the fiine ore with a fluid carbonaceous material andagglomerating the mixture into pellets, all

at a temperature of about 400-500 F. These two steps are preferablycarried out continuously in a suitable pelletizing machine so that theresulting pellets show a uniform cross-section of the ore and binder.

(b) Heating the green pellets to a temperature in the range of 7001000F. to coke the heavy hydrocarbon binder, driving off volatile componentsand resulting in a pellet having coke evenly dispersed therein. Heatingat this stage should be indirect to avoid combustion of the volatiles ordilution thereof with the heating gases.

Further heating the pellet to a temperature in the range of 1500 2200F., during which heating the pellet is hardened and partially reduced.

Optionally, limestone or the like may be added during mixing,particularly if slag-formers are present in the ore, or if either theore or the hydrocarbon contain sulfur or sulfur compounds.

The last heating should of course be carried out in a non-oxidizingatmosphere. Subsequent cooling of the pellets should also be conductedin the absence of air or oxidizing gases, until the pellets reach atemperature where reoxidation is no problem (below about 600 F.).

A variety of hydrocarbon materials may be employed in the process of theinvention. Any heavy residual oil, vacuum residual oil, coal tar pitchor the like may generally be employed; it is desirable that the materialhave a Conradson Carbon content of at least 15% and preferably 20%, andhave a 5% boiling point of at least 650 F. The term 5% boiling pointmeans that 95% of the residual oil boils above the specifiedtemperature. It is further noted that a coal tar pitch would producemore coke and less distillate than the oils discussed hereinbelow and inthe examples.

The pellets produced by the process will vary in composition dependingon the amount of carbonaceous material added and the length of time atthe Various temperatures. It is preferred, however, to produce a pelletreduced about 1540% (25-35% preferred), in terms of total combinedoxygen, in which there is some metallization and little or no freecarbon. Such a pellet is characterized by a very high crushing strengthand a fine porous structure which is eminently suitable for use in ablast furnace or other reduction device. In the case of pellets madefrom taconite or other high-grade concentrates, both the coke rate andfluxing required for reduction in the blast furnace are significant-1yreduced. The amount of metallic iron will not generally exceed about 5%when the pellets are intended for blast furnace usage, but it will beunderstood that by adjustment of oil addition and residence time, asponge iron product can be produced. Preferably, the reduction iscarried out so that the pellet, as discharged from the reducer, containsabout or more FeO, and, as noted above, little or no free carbon andsome metallic iron. If cooling is very slow, it is possible that the FeOwill disproportionate into Fe and Fe O at least according to some priorworkers. Under near equilibrium conditions, a metallic iron content of20% may be achieved. However, under normal (nonoxidizing) gas cooling,which is quite rapid, the FeO structure is substantially retained. Forthis reason the pellet structure is characterized as it is prior tocooling or after rapid cooling. Regardless of cooling rate, pellets ofthe preferred composition have an oxygen-to-iron (weight) ratio in therange of about 0.15 to 0.34.

In FIGURE 1 there is illustrated a very simple embodiment of theinvention illustrating the essential steps thereof. Residual oilpreheated so as to be flowable and ore from a bin are supplied to arotating pelletizing drum. The oil and ore may be separately preheatedto the preferred pelletizing temperature before they are charged, or thepelletizing drum may be provided with heating means. Oil is sprayedcontinuously on the ore, which agglomerates during its passage throughthe pelletizer. Any vapors evolved during this stage are combined withcoker distillate for recovery of valuable constituents.

The pellets discharging from the pelletizing kiln pass through anintermediate hopper and are charged into the coking kiln, which is anindirectly fired travelling grate kiln. In this kiln, the pellets areheated to about 700- 1000 F. and vapors are driven off. The oil vaporsare then passed to a recovery section from an outlet at one end. A sealhopper passes the coked pellets to the hardening and reducing kiln,which in this instance is a directfired, travelling grate kiln, wherethe pellets are heated to 1500-2000 F. or higher. Removal of combustiongases is via a line in the charge end which leads to appropriate solidsremoval and heat recovery equipment (not shown). A travelling grate kilnis preferred for this service as the 1000 F. pellets discharged from thecoker will probably not be hard enough to withstand handling in a rotarykiln.

The hardened pellets pass from the reducing kiln through another sealhopper to a pellet cooler, where their sensible heat is given up withthe production of high-pressure steam. This pellet cooler is providedwith inlets and outlets on the tube side for steam generation, inletsand outlets for supplying an inert or non-oxidizing atmosphere to thepellets, and an outlet for discharging cool pellets 600 F.) to conveyor.The high pressure steam generated in this cooler may be convenientlyutilized to preheat the oil prior to injection into the pelletizing kilnor to drive any rotating equipment.

In FIGURE 2 there is illustrated "a more detailed embodiment of theinvention. As noted above, the formation of green pellets is preferablycarried out in a pelletizing drum and in this embodiment the ore and oilare preheated (not shown) and the drum itself isnot heated. The fines,which are generally at least 70% minus 325 mesh, are conveyed to thepelletizing drum having been mixed with recycle dust and, if desired,limestone prior to preheating. A preheated heavy oil is supplied to thedrums in thegsame manner as illustrated in FIGURE 1. As shown in FIGURE2, recycled solids come from a product screen and a green pellet screen,but it .will be understood that solids will also be collected bycyclones orother equipment from various gas flows. Where appropriate,recycled material should be suitably crushed and ground before chargingto the pelletizing drum.

The oil injection and pelletizing operation is carried out at 400 to 500F. by preheating in order to secure a viscosity of the'residue oilsuitably low to provide an effective. oil spray and to ensure that theoil intimately wets the charging ore and the accreting pellets toachieve uniform dispersion of the carbon for reduction.

-The retention time of the pellets in the balling and mixing apparatusshould be sufiicient to permit the relatively slow growth of balls froman original minuscule size to an eventual /2, or 1 to 1 /2 inch size, asdesired.

When discharged from the pelletizing drum, undersize maybe screened. Atthis stage they have little mechanical strength and must be handledcarefully. The green pellets are conveyed to an indirectly-firedtravelling grate kiln similar to that shown in FIGURE 1 for coking. Ofcourse, any device capable of indirect heating and in which the pelletsare quiescent can be employed. Indirect heating is necessary so that thedistillate can be recovered separately without combustion inside thekiln or dilution with combustion gases. Such'indirect-heated furnacesare well known in the art. Oil distillate passing out of the kiln issent to the recovery unit. The coking kiln is operated at a temperaturewhich will distill essentially all volatile matter out of the pelletsand thoroughly coke the remaining carbon. This is generally in the rangeof 750 to 1000? F., but inthis embodiment a higher discharge temperatureis desirable so that the pellets will be sufiicientlyhard to besubsequently treated in a direct-fired rotating kiln. A two-section kilnmay be employed in this service. The cracked vapors begin to evolve involume at, about 750 F. and resemble in composition those secured ina-conventional delayed coking operation. The non-condensible gaseousportion is rich in methane and hydrogen and, after recovery, is used inthe fuel firing systems, as noted hereinbelow. Since the reduction of FeO to Fe O begins at about 850 F. and does not become appreciable untilabout 1100 is reached, reduction in the coker, even at the higherdischarge temperature, is relatively minor; the major heat requirementsare thus due to sensible heat dutiesand the endothermic cracking ofhydrocarbons in .theresidual oil.

-"Thedistillate may be passed to a condenser where its sensible heat isrecovered, and thence to a knock-out drum from which liquid andnon-condensibles are withdrawn separately or, it may flow directly to afractionating to'wer, without being cooled, and processed as vapors fromdelayed coking drums are normally handled, In most instances a'portionof i the recovered distillate is used f for fuel purposes, andappropriate local storage 'facilitiestnot shown) must be provided.

As noted above, thecoked pellets should have sutficient mechanicalstrength to withstand subsequent handling and treatment by the time,they leave the coking kiln. The e oked pellets are transferred, whilehot, to the charge end of the reducer kiln, where hardening and partialreduc'tion takes place. A hopper seal wherein the pellets form a gassealis preferred. This'kiln is a direct-fired rotating kiln'as shown, butmay be an indirectly or directly"fired"tunnel'kiln' or other suitabledevice capable of maintaining temperatures in the desired 1500-2100 F.

range, 'particularly'if thepellets are still soft. As all of "thereductantis contained in the pellets themselves, the kiln atmosphereneed not be strongly reducing, but of course it should be non-oxidizing.This is readily accomplished by using a deficiency or air in the firingmechanism. Residence time in the reducer kiln will vary,

depending on degree of reduction desired and other factors, but about /2to 2 hours is normal. When'the reducer kiln is directly fired, by meansof a burner located in the discharge end, it may be desirable to injectsome additional air at one or more .points upstream therefrom so thatunburned fuel will be burned and the. entire kiln maintained within thedesired temperature range. This socalled side air injection is wellknown in the art, and is done by mounting a fan on the outside of thekiln shell and blowing air into the kiln interior through a stainlesssteel pipe. Alternatively a substantial portion of the combustion gaseswithdrawn from the charge end can be recycled to the burner end wherethey will mix with the combustion products and provide a more uniformtemperature distribution.

After discharge from the reducer kiln, the pellets are cooled, still ina non-oxidizing atmosphere, to a temperature under 600 F. Below thistemperature surface reoxidation is not a problem, and further cooling isdone with air in a second cooler. Such coolers are of conventionaldesign.

The cooled pellets are then screened, with undersize being recycled tothe pelletizing drum after appropriate grinding. Oversize pellets areready for storage or shipment.

FIGURES 3 and 4 are considered in detail in Example II set forthhereinbelow, but it is of interest to compare them with FIGURES 1 and 2.FIGURES 3 and 4 relate to a plant designed to produce 3000 t.p.d. ofpellets.

On this scale, it is economical to use a fluidized bed heater toinitially heat the concentrate. Further, a separate pellet heater priorto the coker and a calcining stage thereafter are desirable, although interms of actual process ing units it may be desirable to make the pelletheating stage part of the pelletizer or coker, and locate the calciningstage at the end of the coking kiln or the charge end of the reducerkiln.

As shown in FIGURE 3, the liquid recovery section is illustrated asproducing five separate fractions, as might be done in a singlecombination fractionating tower. A small stream may be withdrawn fromthe bottom of the tower and recycled directly to the pelletizer in orderto recycle any ore fines contained in the coker vapors and trapped inthe fractionator liquid streams. This is labeled as a slurry stream inthe drawing, and is distinguished from the heavy oil stream, which isthe highest-boiling wholly liquid stream that is withdrawn. The lighestfraction of gas (tower overhead), comprising noncondensibles andhydrocarbons up to propane (C is shown as being used as fuel in thereducer along with the heavy oil stream; those skilled in the art willappreciate that these streams are utilized separately, the gaseousstream being burned with a substantial deficiency of air to insuremaintenance of a reducing atmosphere.

In the embodiment of FIGURE 3, separate C -400 F. gasoline anddistillate oil streams are withdrawn as byproducts. As shown in ExampleII, the thermal economy of the process is'such that a credit can beobtained from these upgraded products.

The gas and liquid flows for the embodiment of FIG- URE 3 are shown inFIGURE 4. Briefly, incoming air is first preheated by indirect heatexchange against the exhaust gases from the ore preheater and the pelletheater. The air, at about 500 F., is further heated to about 1100" F. ina fired heater. The hot air is passed primarily to the reducer burner,with minor sidesstreams being taken off for combustion in the muflies ofthe calciner and coker.

Coker gas and heavy oil from the liquid recovery still are ditional airbeing added at each stage. Efiluent from the coker mufile is at about1410 F., and is used for heating (without further combustion) in the oreand recycle heaters and in the pellet heater, either in series or inparallel. The combined etiluent, now at about 600 F. and stillcontaining considerable carbon monoxide, which is combustible, is firstused to preheat incoming air, and then, after further cooling to about100 F. (where water vapor is condensed) it is used to cool finishedpellets. The gas is heated to about 1700 F. during the latter operationby the pellets, and is then used as fuel in the air preheater, whichproduces steam as a byproduct. For the conditions set forth in ExampleII, stream production is 150,000 lb./hr.

Understanding of the invention will be facilitated by referring to thefollowing specific examples. Example I presents detailed data on a smallscale operation and Example II provides thermal and material balancesfor a plant producing three thousand tons per day of hardened, partiallyreduced pellets. Example HI discusses the pellet composition and FIGURE5.

EXAMPLE I Eight-hundred pounds of commercially purchased taconiteconcentrate had the composition shown in Table I and sieve analysisshown in Table II.

Table I.Chemical composition The steps of the process were carried outin a batch kiln externally wound with heating cable and equipped toprovide an inert (N atmosphere. Some pre-dried concentrate was chargedand the kiln was preheated to 450 -F. Nitrogen-atomized hot heavy-oilresidue was sprayed in while the kiln was turning at 8 r.p.m., andadditional concentrate was continuously added. The residual oil was atopped crude with an IBP of 700 F., and 14 API gravity and SayboltUniversal viscosity of 320 and 145 seconds at 210 F. and 250 F,respectively. Oil addition was controlled so that, in the finished(coked) pellet, there was 0.092 pound of coke per pound of Fe.

After the pellets attained a satisfactory size (100% plus /1 inch),rotation was stopped and the temperature was raised to and held at,successively, 750, 800 and 865 F. levels. The oil distilled off largelyat the 750 F. level.

The pellets were transferred, while hot, to a horizontal mufile furnaceand heated successively to 1500 F. and 2000 F., again in a nitrogenatmosphere. Considerable weight loss resulted from calcination and oxidereduction.

After 3 hours at 2,000 F., the furnace was turned off 8 and the pelletswere'allowed to cool, the nitrogen atmosphere being retained to preventreoxidation. Y An assortment of the pellets was subjected to crushingstrength tests and chemical analysis. All pellets tested of /2 to /8"size h-ad crushing (i.e. compressive) strength in excess of 300 pounds,as compared to 200-250 pounds exhibited by clay-pelletized taconites.Chemical analysis is set forth in Table III.

Table III.Pellet composition Reduction was about 31%, and in thisinstance the pellet was 80.34% FeO and 9.35% Fe O EXAMPLE II Commercialtaconite ore of the composition shown in Table I of Example I ispreheated to 400 F. and fed continuously into a rotary pelletizer,together with recycle fines. A petroleum residuum fraction having theproperties shown in Table IV is preheated to 400 F. and sprayedcontinuously into the pelletizer.

Table IV.--Petroleum residuum fraction Gravity API 7.4 Conradson carbonNo "percent... 19.6

The resulting green pellets are fed continuously into a travelling gratekiln, wherein the pellet temperature is raised from 400 F. to 750 F. bydirect contact with hot gases. In a subsequent section of this kiln thepellets are further heated to 1000 F. This high temperature portion ofthe kiln is partitioned from the low-temperature section so as tominimize gas fiow or interchange between between the two sections. Inthe high-temperature zone, coking of the pellet binder material takesplace. The cracked vapors are passed to a fractionating tower from whichthe following streams are removed: Colrer Gas (C s and lighter),Gasoline (C(s to 400 BR), Light Distillate Oil (400 to 750 F. BR), andHeavy Distillate Oil (750 to 1100 F. B.R.). Alternatively, of course,the cracked vapors may be just cooled to condense and recover a wideboiling range distillate oil and a fuel gas. Any ore fines entrained bythe coker gases are scrubbed in the bottom of the still and are removedas slurry with some of the still bottoms. This slurry is recycled to thepelletizer.

The coked pellets are fed to a second travelling .grat'e kiln, known asthe calciner, wherein the pellet temperature is increased from 1000 F.to 1600 F. The material is heated indirectly by radiation from anoverhead muffie. The coke binder in the pellets is devolatilized,generating a so-called coker gas which is subsequently used as fuel.Some reduction of the iron oxides in the pellets takes place, generatingCO and CO v The 1600 F. calcined pellets arequite strong andv canwithstand subsequent treatment in a rotary kiln without excessivedecrepitation. The rotary kiln is called the reducer. Here the pelletsare heated by direct radiation from products of combustion to 2000, Thecoke contained in the feed pellets is virtually completely reacted,resulting in the reduction of the iron oxides to lower oxides and asmall amount of iron. This reduction achievesinduration, so that thecooled product pelletsexhibit a big crushing strength, usually exceeding300 lbs.

The reduced and hardened pellets are introduced into the top of a shaftcooler. Here, cool F.) inert gas, free of air or oxidizing gases, ispassed counter-current to the descending pellets, cooling the lattertoapproximately F.

The cooled pellets are screened and the sized product is Many variationsof this processing scheme are possible: conveyed to storage. Theundersize material, about 2% For example, the reducer could be atravelling grate kiln. of the total cooler output, is ground andrecycledto the The temperature levels can be varied considerably,- forore heater. The material flows, to produce 250,000 lb./hr. example, thecalciner pellet discharge temperature could or 3,000 t.p.d. of productpellets, are shown in Table V. 5 be set at 1700 F. instead of l600.F. at=1700 F., sig- The fuel economy ofthis process is demonstrated innificant reduction will occur. Also,,instead of combining the lastcolumn of Table V, which indicates residuum feed the, pellet heater andcoker functions in one travelling of 1.22 bbl. and liquid by-product(gasoline and distilgrate kiln, other combinations are quite possible. 7late oil) recovery of 0.73 bbl. per short ton of product The gas flowpattern can be modified to meet specific pellets. The actual fuel costis further reduced by the dif- 10 plan requirements. All of the 1410 F.gas from t e ke ferential in the per-barrel value of the upgraded liquidmuffie chamber can be passed through the pellet preheat by-product ascompared to the distressed residuum feed- Zone-leaving at about 990 F.(instead of 730 F..); all stock. ormost of this gas can be passedthrough the ore and The fuel economy results from the gas and liquidflow recyc heater- In some cases, it ay be advantageous to system, shownin FIG. 4. The coker gas and calciner gas spill some of the 1410 g tlyto theboiler-air are burned with a deficiency of air (preheated t-opreheater burner to improve temperature control and re- 1'100 F.). Thisis augmented with combustion of the dllee Cooling Water requirementsheavy oil to release the energy required in the rotary kiln Thefollowing advantageous teatllres of the general reducer. The efliuentgas from the reducer is rich in CO, Processing scheme should he noted:Although Wide latidue to the CO content of the products of combustion(the tude ill Processing equipment is Permissible, and desirable gaseousf l b i b d ith a d fi i f i due to variations in ore, residuum, etc.,the use of lowaugmented by the CO generated by the ore reduction. Anattrition devices (such as travelling grate kilns) P to a amount of theffl t gas may be ,recycled the kiln pellet temperature level of 1400- to1800 F. insures low inlet to lower the inlet gas temperature and achievea Pellet degradation ahd'ioW ore y requirements. Use fairly eventemperature distribution in the kiln. This reof indirect heating n t 7F- to about 1500-170Q F. circulation is, however, not always required.range insures fairly complete recovery of gaseous fuels The net reducerefiiuent gas, at about 1865 F., is inand liquid y-p Also, use o reducingatmosphere troduced into the heating chamber of the travelling grate andrelatively uniform temperature in the redheel' Permit l i A li lpreheated i 1100 R) is introduced relatively rapid reduction to proceedto the desired level. into this gas to burn some of the contained CO asrequired deslred action is further aided y the gradual and b h h b lcontinuous release of CO (and equilibrium concentration The calcinereflluent gas, at 1550 F., passes to the of 2) from the surface of thePellet bed, acting as a heating chamberof the coker More preheated(11006 R) gas blanket to prevent excessive contact of the bed with airis introduced, burning a little more of the CO to mainthe combustiongases above the tain heat balance. The gas issues from the mufiled heaths of a relatively reducing gas as the Cooling ing chamber at about 14100About of this medium in the pellet cooler, combined with the relatively14 0 gas is then passed directly through the pellets rapid heat transferdue to direct contact exchange, inon the travelling grate. Four passesare used to achieve sures agalnst Pellet However, good heat countercurrent heat exchange This portion (60%) of covery may be accomplishedwith suitable heat recovery the gas stream leaves the travelling gratekiln (pellet 40 equlpment as shown In heater-calciner) at about 730 F.

The remainder (40%) of the 1410 F. gas leaving the EXAMPLE HI cokermufiled zone is passed through the ore and under- A pellet picked atrandom from those produced in size recycle heatenThis is a shallow-bedfluidized bed Example I was sectioned, mounted and photomicrounit. Thepowder is heated to 400 F., and the gas issues 5 graphed so as todisplay the microstructure resulting from at about 410 F. the process ofthe invention.

TABLE V.MATERIAL FLOWS, 3,000 T.P.D. PELLEI PRODUCTION Ore Recycle Cokerand Li .b ds. Fl

Feed Resid. undersize Green Coked Product calciner Fuel i bbillt oii(dry) material pellets pellets pellets cracked Flow Grav. of prod. gasesrate API pellets Iron oxides 246. 8

- Total 270. 2 Ore/Pellet AnaL:

Fe, Wt. percent- OlFe, Wt.'rati0 Coke/Fe, Wt. ratio N o'rE.-All Flows in1,000s of lbs/hr.

1 The cool gases (730 and 410 F.) are heat exchanged A porous,essentially two-phase structure is present, the

fagainst cool air, thenthey are cooled with water to 100 F. lesser phasebeing gangue materials and the majority of The cooled. gases, stillreducing 'dueto residual CO conthe structure being iron oxide. It isbelieved that the tent, are passed counter-currently through thedescending etching'technique employed selectively removed metallic bedof'pellets-in the pellet cooler. The-gases are thereby iron from thesurface. Macroscopic examinationrevealed heated to about 1685" F.' thatthe cross-section of the pellet was entirely'uniform. The reheated gasesare burned with additional air With the method used it was not possibleto distinguish (cold) to consume the residual C0, and are used toprebetween various iron oxide compositions. I heat-air to the desiredlevel (1100 F;) and to generate It is to be understod that many othermodifications can plant steam. be made to the process illustrated in thedrawings. For

I 11 example, the concentrate and oil can be milled at the 400-500 F.temperature to form an even mixture, and then briquetted or extruded,while hot, in conventional equipment. The green briquettes are thentreated in the same manner as the green pellets. Further, sufiicientcarbonaceous material'can be added to bring about substantially completemetallization, with the production of sponge iron pellets suitable formelting and finishing, for example, in an electric furnace.

The preferred pellet composition, discussed hereinabove, is decidedlyadvantageous, however, for use in a blast furnace. For example, at a 30%reduction level the coke rate in a blast furnace can be 200 lb./ton ofhot metal lower than for unreduced pellets. This drop in the coke rateallows the production rate of the furnace to be increased by about 20%at the same wind rate. The exact degree of reduction desired in anyinstance will depend on economic consideration.

Various other changes in the details, steps, materials and arrangementsof parts, which have been herein described and illustrated in order toexplain the nature of the invention, may be made by those skilled in theart, within the principle and scope of the invention as defined in theappended claims.

The present application is related to copending US. application Ser. No.316,359, filed Oct. 15, 1963, now abandoned, and assigned to the sameassignee.

What is claimed is:

1. A hardened, thermally treated, partially reduced iron-oxide bearingpellet which, prior to cooling or after rapid cooling is characterizedby a finely porous structure and consists essentially of:

at least about 70% FeO;

essentially no free carbon;

O-5% metallic iron;

balance higher iron oxides and impurities;

said pellet being chemically reduced about 15-40%.

2. The pellet as claimed in claim 1, wherein the compressive strength isat least 300 pounds, and size is about /2 to 1 /2 inches in diameter.

3. A thermally treated, partially reduced iron-oxide bearing pelletwhich, prior to cooling or after rapid cooling, is characterized by afinely porous structure and a crushing strength of at least 300 pounds,a size of about h to 1 /2 inches in diameter, and consists essentiallyof:

at least 70% FeO;

-5 metallic iron;

0-5 CaO;

essentially no free carbon;

balance higher iron oxides and impurities;

said pellet being chemically reduced about 25-35%.

4. A hardened pellet consisting of:

0-20% metallic iron;

0-5 CaO;

essentially no free carbon;

balance iron oxides and impurities;

said pellet being characterized by an oxygen-to-iron weight ratio in therange of about 0.15 to 0.34, and having a finely porous structure and acrushing strength of at least 300 pounds.

5. The process for agglomerating and beneficiating an oxide orecomprising:

forming pellets by agglomerating said ore with a heavy hydrocarbon oilhaving a 5% boiling point of at least 650 F., said agglomeration beingcarried out at a lower but still elevated temperature where said oil isfluid;

heating the pellets thus for-med to a temperature between said boilingpoint and the temperature where significant reduction of said ore beginsto occur for a sufiicient time to coke said oil and bake said pellets;

and

further heating said pellets to reducing temperature,

whereby said pellets are hardened and residual carbon therein effectsreduction.

12 6. The process as claimed in claim 5, wherein said pelletizing iscarried out at a temperature in the range of 400 to 650 F. 7'. Theprocess as claimed in claim 5, wherein said coking is carried out at atemperature in the range of 700 to 1000 F.

8. The process as claimed in claim 5, wherein said reduction andhardening are carried out at a temperature in the range of 1500 to 2200F. in a non-oxidizing atmosphere.

9. The process as claimed in claim 7, wherein said coking is carried outin an indirectly fired heater wherein said pellets are in a quiescentstate, and additionally comprising recovering distilled volatiles drivenoff during said coking.

10. The process as claimed in claim 8, wherein said reduction andhardening are carried out in a direct-fired rotary kiln and saidnon-oxidizing atmosphere is provided by burning fuel with a deficiencyof air.

11. The process as claimed in claim 5, wherein the quantity of said oiland said reduction are'controlled to provide a finished pellet reducedabout 15-40%, having 0-5 metallic iron, and essentially no free carbon.

12. The process for producing hardened, prereduced iron oxide pelletsreduced about 15-40% comprising:

forming green pellets by mixing iron ore with a heavy hydrocarbon oil,said oil having a 5% boiling point in the range of about 650 to 1100 F.,at a temperature in the range of about 400 to 500 F.;

coking said green pellets by heating to a temperature in the range ofabout 700 to 1000 F. for a sufficient time to coke the heavyhydrocarbons and permit the cracked volatile constituents of said oil tobe driven off;

hardening and reducing said pellets by heating to a temperature in therange of about 1500 to 2200 F. in a non-oxidizing atmosphere; and

cooling the hardened and reduced pellets in a nonoxidizing atmosphere.

13. The process as claimed in claim 12, wherein said recovered volatilesare utilized to provide endothermic reaction heat.

14. The process as claimed in claim 12, wherein said ore is a taconiteconcentrate.

15. The process as claimed in claim 12, wherein said oil addition andsaid reduction are controlled to produce a pellet containing 0-5%metallic iron and essentially no free carbon.

16. The process as claimed in claim 13, wherein:

volatiles recovered from said coking are fractionated and separate fuelgas and fuel oil fractions are recovered;

said fractions are bur-ned'with a deficiency of preheated air in saidhardening and reducing step;

combustion gases resulting fiom said hardening and reducing step areused to supply heat to said coking step, and to preheat said air andsaid iron ore; and the cooled combustion gases are used to cool saidpellets.

17. The process as claimed in claim 16, wherein combustion gases used insaid cooling step are burned with air, and resulting combustion gasesare utilized to further preheat said air.

18. The process as claimed in claim 16, wherein said coked pellets arecalcined at a'temperature of 1000 to 1600" F. prior to reduction, heattherefor being supplied by combustion gases from said hardening andreducing step. Y t

19. The process as claimed in claim 18, wherein additional preheated airis burned with said combustion gases in said coking and calcining steps.

20. The process as claimed in claim 12, wherein said ore and said oilare separately preheated to 400 to 500 F. prior to formation of saidpellets.

(References on following page) References Cited UNITED STATES PATENTSCulberson et a1. 754

Lesher 754 Peras 75-26 Ban 753 3,341,322 9/1967 Bailey 75--26 3,351,45911/1967 M1115 75-4 L. SEWAYNE RUTLEDGE, Primary Examiner. ERNEST L.WEISE, Assistant Examiner.

US. Cl. X.R. 754, 5

